The present invention relates to a valve operating system for an engine, which includes a cylindrical cam element and switches, by shifting the cam element in one of two camshaft directions, a cam for opening and closing a valve between two valve-opening-and-closing cams which are provided to the cam element coupled to a camshaft in its rotational direction and fitted to be able to shift (move) in the camshaft directions.
Conventionally, a type of valve operating systems for engines is known, which is provided with a plurality of cams having nose portions in different shapes for each valve, and switches an opening degree and open and close timings of at least one of intake and exhaust valves by selecting the cam for opening and closing the valve among the plurality of cams, according to an operating state of the engine.
For example, US2011/0226205A1 discloses a valve operating system. The valve operating system includes a cam element. An end face cam for shifting the cam element is formed in each end face of the cam element in the camshaft directions. A switching member for engaging with one of the end face cams is provided on each of both sides of the cam element in the camshaft directions. The valve operating system switches the cam for opening and closing the valve by actuating the switching member(s) to engage with the end face cams and shifting the cam element in one of the camshaft directions. Moreover, US2011/0226205A1 discloses that the cam element is held at a predetermined position by a detent mechanism.
Each of the end face cams provided to both end faces of the cam element has a protruding portion, and the protruding portion protrudes in one of the camshaft directions from the corresponding end face of the cam element so as to shift (move) the cam element in the corresponding camshaft direction. The valve operating system provided with such a cam element has a disadvantage in that the length of the cam element in the camshaft directions is long, which causes the length of the entire camshaft to be long, particularly in a multi-cylinder inline engine, because a plurality of cam elements are aligned on either one of a camshaft for intake valves and a camshaft for exhaust valves.
It can be considered to shorten a protruding length of each protruding portion of the end face cam in the corresponding camshaft direction as much as possible as a solution for this disadvantage; however, if the protruding length of the protruding portion is shortened, the cam element cannot be shifted enough, and the cam for opening and closing the valve may not be able to surely be switched.
The present invention is made in view of the above situations and reduces the length of a valve operating system in the camshaft directions as much as possible by shortening protruding lengths of protruding portions of end face cams provided to both end faces of a cam element within an extent that a valve-opening-and-closing cam can be surely switched.